StreamBuilder doesn't rebuild after Navigator.pop - flutter

Question

I have a simple service which is tracking the current user position :
class LocationService {
LatLng _lastLocation;
Location location = Location();
StreamController<LatLng> _locationController = StreamController<LatLng>();
Stream<LatLng> get locationStream => _locationController.stream;
LocationService() {
location.onLocationChanged().listen((locationData) {
LatLng location = LatLng(locationData.latitude, locationData.longitude);
if(_lastLocation == null || _lastLocation != location) {
_lastLocation = location;
_locationController.add(location);
}
});
}
}
Then, I'm using this service to create a Map (thanks to flutter_map) which is following the current user position :
class SelfUpdatingMap extends StatelessWidget {
final Icon currentPositionIcon;
final MapController _controller = MapController();
SelfUpdatingMap({
this.currentPositionIcon,
});
#override
Widget build(BuildContext context) => StreamBuilder<LatLng>(
stream: LocationService().locationStream,
builder: (context, asyncSnapshot) {
if (asyncSnapshot.hasError || asyncSnapshot.data == null) {
return Text('Loading...');
}
try {
_controller?.move(asyncSnapshot.data, 18);
} catch (ignored) {}
return _createMapWidget(context, asyncSnapshot.data);
},
);
Widget _createMapWidget(BuildContext context, LatLng location) => FlutterMap(
options: MapOptions(
center: location,
zoom: 18,
),
layers: [
TileLayerOptions(
urlTemplate: 'https://{s}.basemaps.cartocdn.com/rastertiles/voyager/{z}/{x}/{y}.png', // https://a.tile.openstreetmap.fr/osmfr/{z}/{x}/{y}.png is good too.
subdomains: ['a', 'b', 'c'],
),
MarkerLayerOptions(
markers: [
Marker(
width: 40,
height: 40,
point: location,
builder: (contact) => currentPositionIcon,
),
]
),
],
mapController: _controller,
);
}
Then, I use the SelfUpdating widget in two places :
The page 1, ancestor of page 2.
And in the page 3, successor of page 2.
So here is the situation :
I launch my app, I'm on the page 1. I have my SelfUpdatingMap.
I call Navigator.pushNamed(context, '/page-2').
I call Navigator.pushNamed(context, '/page-3'). I have another SelfUpdatingMap.
I call two times Navigator.pop(context), I get the page 1 BUT the SelfUpdatingMap doesn't update itself anymore.
The builder is not even called anymore. So please, what is wrong with this code ?
Thank you !

Answer 1

When you push and after pop a page, the build metod doesn't restart.
I found the same problem with the FlutterBluetoothSerial.instance.onStateChanged() stream and the solution that I found is to add the stream to a local static final variable and use it instead of calling every time the original method (you can do that only if the stream is a broadcast one I think).
Solution example:
class ExampleClass {
static final Stream<LatLng> locationStream = LocationService().locationStream;
}
class SelfUpdatingMap extends StatelessWidget {
...
#override
Widget build(BuildContext context) => StreamBuilder<LatLng>(
stream: ExampleClass.locationStream,
builder: (context, asyncSnapshot) {
if (asyncSnapshot.hasError || asyncSnapshot.data == null) {
return Text('Loading...');
}
try {
_controller?.move(asyncSnapshot.data, 18);
} catch (ignored) {}
return _createMapWidget(context, asyncSnapshot.data);
},
);
...
}
class Page3Widget extends StatelessWidget {
...
#override
Widget build(BuildContext context) => StreamBuilder<LatLng>(
stream: ExampleClass.locationStream,
builder: (context, asyncSnapshot) {
//do something
},
);
...
}